1. desertion, abandonment, defection -- (withdrawing support or help despite allegiance or responsibility; "his abandonment of his wife and children left them penniless")
2. apostasy, renunciation, defection -- (the state of having rejected your religious beliefs or your political party or a cause (often in favor of opposing beliefs or causes))

1.

Kitty and Lydia take his defection much more to heart than I do. - from Pride and Prejudice by Jane Austen

2.

Had their defection from the traditions of the Tharks been discovered both would have paid the penalty in the great arena before Tal Hajus and the assembled hordes. - from A Princess of Mars by Edgar Rice Burroughs

3.

I now knew that while theoretically a prisoner I was virtually free, and I hastened to regain the city limits before the defection of Woola could be discovered by his erstwhile masters. - from A Princess of Mars by Edgar Rice Burroughs